1. Field of the Invention
The present invention relates to apparatus and methods of manufacture of ferric sulfate. In particular, the present invention relates to batch-style processes in which ferric sulfate is produced from a single pressure vessel. Additionally, the present invention relates to processes for the manufacture of ferric sulfate which avoid the introduction of external heat to the process.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Ferric sulfate [Fe2(SO4)3] is a commonly-used material of commerce. It finds use in, for example, potable water and sewage treatment processes, where it acts as a flocculant to remove suspended particles in the water. Furthermore, ferric sulfate is a useful precursor to other commonly-used materials of commerce. For example, roasting of ferric sulfate yields ferric oxide and sulfur trioxide gas, while hydration of sulfur trioxide gas yields sulfuric acid.
In the past, ferric sulfate has been produced in a one or two staged process. Initially, the iron ore is mixed with water and sulfuric acid in a digester container. This digester container is heated to approximately 230° F. and exposed to atmospheric pressure. The product of this process is ferrous sulfate and ferric sulfate which is then passed to an oxidizer. The oxidizer is a separate pressure vessel that allows oxygen to be introduced to the ferrous sulfate at approximately 60 p.s.i. As a result, ferric sulfate is produced as a product of this process.
Unfortunately, this process is relatively expensive. Initially, a pair of vessels can be required for the process. The digester is a relatively large vessel that can occupy a great deal of space within a production facility. The oxidizer is a relatively expensive pressure vessel. Since heat may be applied to the digester, the cost of fuel used to heat the digestion process can be considerable. As such, the prior art process that are employed for the production of ferric sulfate do not optimize the cost and capital expenditure associated with the production of such ferric sulfate.
In the past, various patents have issued relating to the production of ferric sulfate. For example, an early patent was U.S. Pat. No. 2,196,584, issued to A. E. Edison on Apr. 9, 1940. This patent describes a process for producing ferric sulfate in which ferrous sulfate is slurried in a sulfuric acid solution to make a slurry containing no substantial excess of water over that required to make the slurry fluid at all times. The ferrous sulfate in the slurry is oxidized with nitric acid. The oxidation occurs at a temperature above about 60° C.
U.S. Pat. No. 2,252,332, issued on Aug. 12, 1941 to J. K. Plummer, shows a process of making ferric sulfate in which iron sulfide ores are roasted in a furnace. The dust from the furnace gasses that contain insoluble ferric oxide are collected and mixed with sulfuric acid. Water is added to the mixture. The mixture is stirred without the application of external heat until the reactor is raised to a temperature of approximately 310° F. The heat of reaction is held within the mixture by placing it in a heat-insulated chamber.
U.S. Pat. No. 2,306,425, issued on Dec. 29, 1942 to J. G. Bevan, provides a process for the production of ferric sulfate in which an aqueous solution of ferric sulfate is passed downwardly through a packed tower containing metallic iron so as to reduce the iron of the ferric sulfate and oxidize the metallic iron with the production of a solution of ferric sulfate in the upper portion of the tower. Gases containing sulfur dioxide and oxygen are passed upwardly through the tower in contact with the downwardly flowing solution so as to oxidize the ferrous sulfate and produce a solution in ferric sulfate in a lower portion of the tower.
U.S. Pat. No. 3,954,953, issued on May 4, 1976 to Satterwhite et al., describes an energy-conserving process for the manufacturing of ferric sulfate. At an initial aqueous phase of the process, a low water-containing slurry or dispersion of iron oxide is reacted with only a portion of the total sulfuric acid required in the process to produce a ferric sulfate-containing slurry having unreacted iron oxide. A quantity of acid withheld from the aqueous phase is employed at the time of agglomeration of the ferric sulfate-containing slurry. The delay of the use of the remaining acid to a later step in the process allows the heat of reaction generated in the conversion of the unreacted iron oxide in the slurry to be utilized for completing the reaction and for drying the granules.
U.S. Pat. No. 4,036,941, issued on Jul. 19, 1977 to Boyles et al., shows the preparation of ferric sulfate solutions by a process for recovery of iron from an iron mud. The iron mud contains a mixture of gypsum and ferric hydroxide. The gypsum and the ferric hydroxide mixture is contacted with sulfuric acid of a concentration between 93 and 98 percent for a period of one to twelve hours. The undissolved material is removed and recovered as a 25 to 50 percent ferric sulfate solution.
U.S. Pat. No. 4,707,349, issued on Nov. 17, 1987 to N. B. Hjersted, provides a process of preparing a preferred ferric sulfate solution and product. Iron oxides or iron are dissolved in sulfuric acid to form ferrous sulfate. The ferrous sulfate is partially oxidized to ferric sulfate in the presence of dissolved oxygen. In a second stage of oxidation, the remaining ferrous sulfate is oxidized to ferric sulfate by the action of a non-molecular oxygen-oxidizing agent, such as hydrogen peroxide. During both stages of oxidation, a catalyst, such as copper sulfate or copper ammonium sulfate, is used.
U.S. Pat. No. 4,814,158, issued on Mar. 21, 1989 to N. R. Everill, describes a process for making liquid ferric sulfate from finely-divided ferric oxide, sulfuric acid and water. This is carried out in a closed reaction vessel at temperatures ranging from about 130° C. to about 150° C. and at pressures from about 30 p.s.i. to about 40 p.s.i. The reaction time ranges from four to eight hours.
U.S. Pat. No. 5,194,240, issued on Mar. 16, 1993 to J. R. Derka, provides the process of the manufacture of ferric sulphate from ferrous sulphate in a closed circuit or vessel having a liquid phase and a vapor phase. The vapor phase is a closed system. The process provides oxidation between about 70° C. to about 150° C. of the iron under pressure utilizing oxygen in the closed circuit and NOx as a catalyst. U.S. Pat. No. 5,332,565, issued on Jul. 26, 1994 to J. R. Derka, shows a similar process as that of U.S. Pat. No. 5,194,240,
U.S. Pat. No. 5,624,650, issued on Apr. 29, 1997 to McEwan et al., shows a nitric acid process for ferric sulfate production. Ferric sulfate is produced by treating ferric ammonium sulfate, ammonium jarosite, or a similar iron complex with nitric acid. The ferric ammonium sulfate or ammonium jarosite can be formed by treating a sulfuric acid leaching solution with a solution of ammonium nitrate. Upon addition of dilute nitric acid at a temperature of about 60° C., ferric sulfate forms and is recovered.
U.S. Pat. No. 5,766,566, issued on Jun. 16, 1998 to Mattila et al., provides a process for preparing ferric sulfate by forming a slurry which contains ferrous sulfate and sulfuric acid. The slurry contains bivalent iron in both the solution phase and the solid phase. The slurry is oxidized to form a ferric sulfate slurry. The ferric sulfate slurry is solidified to form solid ferric sulfate.
U.S. Pat. No. 6,375,919, issued on Apr. 23, 2002 to Kakio et al., teaches a method for the manufacture of ferric sulfate solution and a water treatment agent using the same. Iron ore containing 30 percent of FeOOH as a trivalent iron is calcined at 200-600° C. and then dissolved in sulfuric acid.
U.S. Pat. No. 7,067,100, issued on Jun. 27, 2006 to Faigen et al., describes a liquid ferric sulfate manufacturing process. This liquid ferric sulfate is produced from finely-divided ferric oxide, sulfuric acid and water in a closed reaction vessel at temperatures ranging from about 130° C. to about 150° C. and pressures from about 30 p.s.i. to about 70 p.s.i. The reaction time ranges from four to eight hours and produces liquid ferric sulfate having at least 10 percent trivalent iron. U.S. Pat. No. 7,387,770, issued on Jun. 17, 2008 to Wilkinson et al., shows a process similar to that of U.S. Pat. No. 7,067,100
It is an object of the present invention to provide a method for manufacturing ferric sulfate in which the digestion and oxidation processes can occur in a single operation.
It is another object of the present invention to provide a process for the production of ferric sulfate in which the ferric sulfate is produced economically and optimally.
It is another object of the present invention to provide a process for the production of ferric sulfate that allows ferric sulfate to be produced from hematite without introduction of oxygen.
It is still another object of the present invention to provide a process for the manufacture of ferric sulfate which minimizes heat addition from external sources.
It is still a further object of the present invention to provide a process for the manufacture of ferric sulfate that reduces the time for digestion.
It is still another object of the present invention to provide a process for the manufacture of ferric sulfate which allows the process to be carried out in a single vessel without the need for separate vessels for digestion and oxidization.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.